This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 100 35 349.5, filed on Jul. 20, 2000, the entire disclosure of which is incorporated herein by reference.
The invention relates to an aircraft door comprising at least a door framing and an outer skin connected therewith, which takes up pressure loads.
An aircraft comprises, as a rule, a passenger door, a freight gate and/or a freight trap door. The passenger door, the freight gate and the freight trap door are referred to in the following text by the term: door. The door has a wall hereinafter referred to as outer skin which conforms itself to the surrounding surface contour of an aircraft fuselage when the door is in the closed position, so that a seamless transition exists between the fuselage surface and the outer skin. This conforming of the outer skin to the fuselage contour exists in the circumferential direction of the fuselage and in the longitudinal direction of the fuselage.
The outer skin is connected to a door framing that provides the required stiffness to the outer skin. The door framing forms an internal door structure and must be distinguished from a door frame that surrounds a door opening in the fuselage. The outer skin forms an uninterrupted surface, which during flight does not produce any additional drag, while safely sealing the door opening of the aircraft fuselage. The outer skin corresponds to a so-called load bearing section or part of the door which is exposed to dynamic loads. This means, that during flight the outer skin must take-up pressure loads and aerodynamic loads. Pressure loads occur due to the pressure difference between the cabin interior and the outer atmosphere. Aerodynamic loads are, for example caused by vortices or atmospheric flows along the outer surface of the aircraft body. The outer skin of the door is, however, also exposed to so-called operating loads which are caused, for example by the preparation for passenger entering or leaving the aircraft when a stair or freight chute must be positioned to face the door. These operating loads may, in the most adverse instance, damage the outer skin. Such damage may, in the long run, be a cause for material failures of the outer skin during flight.
The outer skin of known doors is made of sheet metal having a substantially constant material thickness which is connected by rivets to the door framing. Other doors are also known wherein the outer skin and the door framing are manufactured as a single piece by casting. In both instances a door operating mechanism is installed in the intermediate spaces of the door framing. The operating mechanism includes electrical and mechanical subassemblies at least for opening and closing the door. The door framing is covered on its side facing into the cabin by a cladding. The cladding is a so-called no load bearing section or part of the door, which, compared to the outer skin need to take up substantially smaller loads. It is a disadvantage of known doors that they have a relatively large weight and that they cause relatively high production cost.
It is an object of the invention to further and noticeably reduce the weight of an aircraft door while satisfying the safety requirements and to also lower the manufacturing cost relative to known doors. Another object of the invention is to vent the inner space of an aircraft door to the outer atmosphere.
The outer skin of the present aircraft door is displaced radially inwardly relative to the surface contour of the fuselage, i.e. lowered or offset in the direction of the fuselage interior. Thus, a trough is formed. This trough or the inwardly displaced, offset surface of the outer skin is covered by a planking in an aerodynamically advantageous manner. For aerodynamic reasons the planking itself is adapted to the surface contour of the fuselage. The planking does not completely seal the trough formed by the outer skin. There should remain a venting connection in the form of a small covered vent opening, or of a small vent tube, or channel in order to achieve a pressure equalization inside the trough relative to the outer atmosphere that surrounds the aircraft. Thus, the offset outer skin which according to the invention forms the bottom of the trough continues to be exposed to the pressure difference between the outer atmosphere and the inner cabin pressure so that substantial pressure loads are kept off the planking that covers the trough outwardly except for the vent which assures that atmospheric pressure prevails on both sides of the planking.
It is an advantage of the invention that displacements caused by the pressure load gradient on the outer skin cannot be adversely effective in an aerodynamic sense on the outer skin. No additional measures need to be taken in order to noticeably reduce these displacements, whereby the effort and expense for manufacturing the door is reduced.
The invention has the further advantage that the effort and expense for a thermal insulation of the door can be noticeably reduced, because the trough shaped hollow space between the outer planking and the xe2x80x9couterxe2x80x9d skin or rather the trough bottom can be used as an additional insulation.
Furthermore, the door operating mechanism for opening and closing the door can be installed advantageously in the trough shaped hollow space between the stiffening members forming the door framing. This door framing is at least connected with the outer skin or trough bottom and can carry or hold, for example, the outer planking.
According to a further embodiment of the invention only the outer skin itself is offset inwardly without also offsetting a skin flange extending in a circumferential direction around the trough. The skin flange of the outer skin is adapted to the surface contour of the fuselage to extend flush with the surface contour. A stiffening is achieved by this xe2x80x9ctrough shapedxe2x80x9d configuration of the outer skin, whereby it becomes possible to avoid rib elements that were required heretofore. The present doors require either ribs or beams to form the framing but not both ribs and beams. This feature brings an advantage in the weight reduction and in the manufacturing.
In connection with this embodiment, the planking can merge into the contour of the flange of the outer skin. The planking would, in this case, only cover the surface of the offset outer skin but not the skin flange.
According to a further embodiment it would, however, be possible that the planking also fully covers the skin flange of the outer skin. The flange, thus, would also be offset somewhat inwardly relative to the surface contour of the fuselage. Thus, the planking could itself fit into the surface contour of the fuselage.